The present invention relates to a micromechanical component, in particular an acceleration sensor, having a flexible spring device for the spring mounting of a mass over a substrate, the flexible spring device being connected on the one hand with the mass and on the other hand being anchored in the substrate.
Although applicable to arbitrary micromechanical components and structures, in particular sensors and actuators, the present invention, as well as the problem on which it is based, is explained in relation to a micromechanical acceleration sensor that can be manufactured in silicon surface micromechanical technology.
Acceleration sensors, and in particular micromechanical acceleration sensors in surface micromechanical or volume micromechanical technology, are gaining increased market share in the area of motor vehicle equipment, and are increasingly replacing the previously standard piezoelectric acceleration sensors.
Standardly, the known micromechanical acceleration sensors operate in such a manner that, upon being deflected, the spring-mounted seismic mass device, which can be deflected in at least one direction by an external acceleration, effects a change of capacitance in a differential capacitor device connected therewith, this change being a measure of the acceleration.
The sensitivity of such known micromechanical acceleration sensors, e.g. for the measurement quantity acceleration, is currently set essentially by the rigidity of the spring mounting of the seismic mass, i.e., by the spring constant thereof. The associated specific integrated electrical circuit (ASIC) permits adjustment only in a relatively small range of sensitivity.
Micromechanical acceleration sensors for maximum accelerations between e.g. 2 g and 50 g (where g=acceleration due to gravity) are currently set only through differing spring rigidities; here, as a rule, there is little variation in the seismic masses.
Thus, in the known acceleration sensors it has turned out to be disadvantageous that different layouts are required for different maximum accelerations, and adjustment is possible only within a very small range.
The micromechanical component according to the present invention, having the features of claim 1, has the advantage that the spring rigidity can be adjusted in gradual fashion in a pre-measurement stage or a final measurement stage, so that a single layout or design can be used for a wide range of rigidities.
The idea on which the present invention is based is that in the micromechanical component, a structure that is or can be mechanically fixed, formed as a spring, can be unlocked or locked in order to set the effective rigidity of the flexible spring device in step-by-step fashion. For this purpose, two or more spring elements, having the same or different rigidities, are situated in series and/or in parallel, and a desired effective spring constant is set.
In the subclaims, advantageous developments and improvements of the micromechanical component indicated in claim 1 are given.
According to a preferred development, the mass is connected with a first spring element that can be moved in relation to the substrate, and is connected with one end of a second spring element via a first connecting web. At the first connecting web, a first anchoring structure that can be isolated is provided, for the isolatable anchoring of the first connecting web in relation to the substrate. In this way, an adjustable connection in series of at least two spring elements can be realized.
According to a further preferred development, the first isolatable anchoring structure has at least one first isolation region that can be isolated through the application of electrical current. This is a useful method for disconnecting a mechanical connection by melting, in a manner comparable to an electrical fuse.
According to a further preferred development, the first isolatable anchoring structure has two first isolation regions, which are provided at two opposite sides of the first connecting web. In this way, a stable, symmetrical anchoring can be realized.
According to a further preferred development, the second spring element is connected with one end of a third spring element via a second connecting web. At the second connecting web, a second isolatable anchoring structure is provided for the isolatable anchoring of the second anchoring web in relation to the substrate. In this way, additional spring elements can be connected in series in an analogous fashion.
According to a further preferred development, the second isolatable anchoring structure has at least one second isolation region that can be isolated through the application of electrical current.
According to a further preferred development, the second isolatable anchoring structure has two second isolation regions that are provided at two opposite sides of the second connecting web.
According to a further preferred development, the respective first and/or second isolation region has a first current line that is connected with the relevant isolatable anchoring structure, and a second current line that is connected with the flexible spring device, preferably with an anchoring thereof. In this way, the isolating current connection can be realized without a large additional expense.
According to a further preferred development, the first and second isolation region, or the first and second isolation regions, have different first current lines, so that they can be isolated selectively.
According to a further preferred development, the first and second isolation region, or the first and second isolation regions, have the same first current line and have different cross-sections, so that they can be selectively isolated. This design saves the provision of different first current lines for the isolation.
According to a further preferred development, the mass is connected with a first spring element that can be moved in relation to the substrate, and is connected, via a first connecting web, with one end of a second spring element. At the first connecting web, a first controllable anchoring structure is provided for the controllable anchoring of the first connecting web in relation to the substrate. A controllable anchoring structure has the advantage that it can be switched between the locked and unlocked states in reversible fashion. Moreover, in this way, in principle a continuous controlling (i.e., without gradations) of the effective spring constant is possible.
According to a further preferred development, the first controllable anchoring structure has at least one first isolation region that can be controlled by a generator device for a magnetic or electrical field. In this way, a contactless controlling can be achieved.
According to a further preferred development, the first controllable anchoring structure has two first isolation regions that are provided at two opposite sides of the first connecting web.
According to a further preferred development, the second spring element is connected, via a second connecting web, with one end of a third spring element. At the second connecting web, a second controllable anchoring structure is provided for the controllable anchoring of the second connecting web in relation to the substrate.
According to a further preferred development, the second controllable anchoring structure has at least one second isolation region that can be controlled by a generator device for a magnetic or electrical field.
According to a further preferred development, the second controllable anchoring structure has two second isolation regions that are provided at two opposite sides of the second connecting web.